Nickel-chromium alloys with chromium contents of 40% by weight or more have extremely low ductility. An improvement in both strength and ductility by casting of such high chromium content alloys was totally unexpected.
The use of spray casting in the formation of metal alloys having a low chromium content is generally well known. Such process involves the use of an atomizing gas to which the molten alloy is exposed as disclosed for example in U.S. Pat. Nos. 4,117,209, 4,606,948, 4,977,950, 5,017,250, 5,154,219, 5,489,417 and Re. 31,767, respectively issued to Markin et al., Hajmrle et al., Muench, Ashok, Watson et al., (2), and Brooks. U.S. Pat. No. 4,779,802 to Coombs is of interest in regard to spray forming atomization. Only the foregoing referred to Markin et al. and Hajmrle patents also relate to use of the spray casting process for nickel-chromium types of alloys, expressly limited to low content chromium of 20% by weight or less. The production of Nickel-chromium alloy is also disclosed in U.S. Pat. No. 5,843,587 to Nakamori for use as a gas turbine blade coating without regard to increasing alloy strength. The spray casting process was not heretofore expected to produce a metallic nickel type of alloy having the advantage of high ductility in connection with a high chromium content in excess of 40% by weight.
It is therefore an important object of the present invention to provide a method for producing a metallic alloy with a high chromium content, having an increase in both strength and ductility despite the normally expected presence of brittleness associated with high chromium content alloys.